Chromatography is a widely used analytical technique for the chemical analysis and separation of molecules. Chromatography involves the separation of one or more analyte species from other matrix component present in a sample. A stationary phase of a chromatography column is typically selected so that there is an interaction with the analyte. Such interactions can be ionic, hydrophilic, hydrophobic, or combinations thereof. For example, the stationary phase can be derivatized with ionic moieties that ideally will bind to an ionic analytes and matrix components with varying levels of affinity. A mobile phase is percolated through the stationary phase and competes with the analyte and matrix components for binding to the ionic moieties. The mobile phase is a term used to describe a liquid solvent or buffer solution that is pumped into a chromatography column inlet. During this competition, the analyte and matrix components will elute off of the stationary phase as a function of time and then be subsequently detected at a detector. Examples of some typical detectors are a conductivity detector, a UV-VIS spectrophotometer, and a mass spectrometer. Over the years, chromatography has developed into a powerful analytical tool that is useful for creating a healthier, cleaner, and safer environment where complex sample mixtures can be separated and analyzed for various industries such as water quality, environmental monitoring, food analysis, pharmaceutical, and biotechnology.
Under certain circumstances, a sample can have a relatively high concentration of a matrix component compared to the analyte concentration. This can cause an interference and prevent an accurate analysis of the analyte within the sample. In one instance, an excessively high matrix concentration can saturate the conductivity detector skewing the baseline response of the analyte peak of a chromatogram. In another instance, a matrix component can generate a chromatographic peak that overlaps with the analyte peak, and thus, interfere with the analysis. An example of matrix species can be sodium chloride in the trace analysis of perchlorate. As such, the liquid sample will typically be pre-treated to remove or reduce a high concentration of a matrix ion like chloride.
Solid phase extraction is a type of sample pre-treatment that can be used to remove matrix chemicals from a sample. Some solid phase extraction devices require a significant amount of pressure to pass a liquid sample through the solid phase extraction device, which is not well-suited to automated sample pre-treatment with auto-samplers. Other solid phase extraction devices that do not require a significant amount of pressure cannot bind a significant amount of matrix chemicals because of low capacity. It should also be noted that the binding capacity per unit volume of the extraction device needs to be sufficiently large so as to reduce the proportion of the dead volume of the extraction device where the liquid sample cannot be easily recovered. A relatively low dead volume is useful where there is a limited volume of a sample to pre-treat. Thus, Applicant believes that there is a need for solid phase extraction materials that have a high capacity per unit volume sufficient to pre-treat a single sample, require a relatively low pressure, and have a compact size so that it can be adapted to existing auto-sampling instruments.